Multiwavelength monitoring of the unusual ultraluminous supernova SN 1978K in NGC 1313 and the search for an associated gamma-ray burst

I. A. Smith*, S. D. Ryder, M. Böttcher, S. J. Tingay, A. Stacy, M. Pakull, E. P. Liang

*Corresponding author for this work

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

We discuss our radio (Australia Telescope Compact Array and Australian Long Baseline Array) and X-ray (XMM-Newton) monitoring observations of the unusual ultraluminous supernova SN 1978K in NGC 1313 at ∼25 yr after the explosion. SN 1978K is a rare example of a Type IIn supernova that has remained bright enough to have long-term X-ray and radio observations. The observations probe the dense medium that was ejected by the progenitor star prior to its explosion; the star might have been a luminous blue variable. The radio imaging shows that the source remains compact, but it may be marginally resolved. The radio monitoring shows deviations from a smooth decay, suggesting that inhomogeneities are present in the radio-emitting region. It appears that a major change occurred in the mass-loss rate of the progenitor star shortly before the supernova event. The X-ray emission between 2000 and 2006 is consistent with the radiation coming from two shocks. All the X-ray data can be fit using the same model (with no systematic evolution or short-term variability), but this has a surprising requirement: the X-ray-emitting regions have a very large abundance of helium. This would be consistent with the X-ray-emitting shocks being located in a helium-rich layer that was ejected by the progenitor star, or helium-rich material was ejected in the supernova explosion. The unusual properties of the supernova motivated a search for an associated gamma-ray burst (GRB). We show that SN 1978K was inside the ∼4 σ error box of GRB 771029. If this association is correct, the GRB was exceptionally underluminous. However, the quality of the gamma-ray burst locations at that time was poor, and this is likely just a chance alignment.

Original languageEnglish
Pages (from-to)1130-1137
Number of pages8
JournalAstrophysical Journal
Volume669
Issue number2
DOIs
Publication statusPublished - 10 Nov 2007
Externally publishedYes

Keywords

  • Galaxies: individual (NGC 1313)
  • Gamma rays: bursts
  • Supernova remnants
  • Supernovae: individual (SN 1978K)

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